The present invention relates generally to high-persistence display circuit elements and, more particularly, to a circuit, and associated method, which minimizes interference caused by slow image decay rates characteristic of such high-persistence display elements.
Many electronic devices include, as portions thereof, visual display elements which permit the visual display of information upon display screens thereof. The information displayed by such display elements may include, for example, information generated during operation of the electronic devices and information indicative of operation of the electronic devices. Because the information is displayed by the visual display elements in visual form, viewers of such elements are able to discern quickly and readily the information display thereupon. Examples of visual display elements include indicating lights, light emitting diodes, and liquid crystal displays.
Advancements in the field of electronics has permitted miniaturization of the electronic circuitry comprising electronic devices as well as permitting the introduction of an ever-increasing array of new types of electronic devices. Radio communication devices, such as radio telephones operative in a cellular communication system, are examples of electronic devices comprised of electronic circuitry which have been increasingly miniaturized.
Concomitant with the reduction in the physical dimensions of the electronic circuitry of the electronic devices has been a similar reduction in the physical dimensions of the housings, and other structure of such electronic devices. As the resultant electronic devices are of increasingly smaller physical dimensions, visual display elements forming portions of such electronic devices must also be of increasingly smaller physical dimensions.
However, the visual display elements must be large enough to permit visual display of information in a form permitting convenient viewing thereof by viewers of such displays.
Because of such reduced physical dimensions permitted of the visual display elements of the electronic devices, and because the size of the visual display elements must remain large enough to permit viewers convenient viewing of the information displayed thereupon, an increasing number of instances occur in which the display devices are of physical dimensions which do not permit the entire amount of information which is desired to be displayed upon the display element to be displayed thereupon at any particular instance.
When the information to be displayed is comprised of alphanumeric information, the information desired to be displayed upon the display elements may be caused to be scrolled upon the display screens of the display elements in manners analogous to the display of stock market information on a stock market ticker-tape.
While information displayed upon a display element in such a manner appears to be scrolled upon the display screen of the display element, such an effect is actually created by sequentially displaying upon the display screen of the display element a plurality of discrete image frames. In a manner quite analogous to the manner in which individual frames of a movie reel, when displayed sequentially at a rapid display rate, appear to generate a single, moving picture, the alphanumeric display is caused to appear to scroll across the display element.
As noted briefly hereinabove, a liquid crystal display device is operative to form a visual display element. Use of a liquid crystal display device is of particular advantage as a liquid crystal display device requires little operative power to generate a visual display. When an electronic device is powered by a portable power supply, minimization of amounts of power required to operate the device is normally desired. Accordingly, use of a liquid crystal display device as a visual display element when power consumption of a device is to be minimized oftentimes occurs.
A visual display is generated upon a liquid crystal display device by applying low voltage signals to portions thereof. By applying a low voltage signal to various portions of the liquid crystal display device, the polarity of the affected portions of the device is altered. Changes in the polarity of the affected portions of the device affect the reflectivity and transmissivity characteristics, and, hence, thereby alter the visual characteristics, of the affected portions of the device. By selectively applying voltages to desired portions of the device, thereby to alter the visual characteristics of the desired portions of the device, alphanumeric symbols are formed.
However, upon termination of application of the voltages to the selected portions of the liquid crystal display device, the visual characteristics of the affected portions of the device do not instantaneously change. Rather, an image decay rate is associated with the affected portions of the device. That is to say, the visual characteristics of the device are altered only gradually upon termination of application of the voltages thereto. Only after a time period, related to the image decay rate, are the visual characteristics of the device, previously altered by application of the voltages thereto, no longer visible.
Other constructions of display elements similarly exhibit such characteristics. Display devices exhibiting such characteristics are sometimes referred to as slow-decay displays or high-persistence displays. A liquid crystal display device, or other super-twist display device, is one such example of a slow-decay display or high-persistence display.
When application of voltages associated with a first image frame displayed by the liquid crystal display device is terminated, and voltages associated with a subsequent image frame are applied to the device prior to disappearance of the previously generated image frame, the previously-generated image frame interferes with the visual appearance of the subsequently generated image frame. Such interference is also sometimes referred to as image runover or, more simply, runover. Such interference degrades the quality of the image scrolled upon the display device.
What is needed, therefore, is an improved apparatus, and associated method, which minimizes interference between sequentially-generated image frames displayed upon a high-persistence display device.
A portable radiotelephone utilized in a cellular communication system is one type of electronic device which sometimes includes a liquid crystal display device. The problems associated with the image decay rate of a liquid crystal display is similarly exhibited in a liquid crystal display device forming a portion of the radiotelephone.
What is further needed, therefore, is a display circuit, and a radiotelephone including such, which minimizes interference between sequentially generated image frames which are displayed by the display circuit.